Technical Field
The present disclosure relates to an electrochromic material for a display device, and more particularly, to an electrochromic material having an excellent transmittance and an excellent blocking degree, and an electrochromic particle, a transmittance variable panel and a display device including the electrochromic material.
Description of the Related Art
As an information society progresses, a request for a flat panel display of an excellent image increases. Among various flat panel displays, a liquid crystal display (LCD) device and an organic light emitting diode (OLED) display device have been the subject of recent research.
The LCD device displays an image using an optical anisotropy and a polar property of a liquid crystal molecule. For example, the LCD device may include a first substrate having a pixel electrode and a common electrode, a second substrate facing the first substrate and a liquid crystal layer including the liquid crystal molecule between the first and second substrates. The OLED display device displays an image using an emission of an emitting layer. For example, the OLED display device may include an anode, a cathode facing the anode and an emitting layer between the anode and the cathode. A hole injected from the anode and an electron injected from the cathode are combined to form an exciton, and the exciton transitions from an excited state to a ground state to emit a light.
Recently, a transparent display device a whole of which is transparent has been suggested. Specifically, the transparent display device may be used as a window type display device such as a smart window. However, since the transparent display device does not have a black state, a contrast ratio and a visibility of the transparent are reduced.
To improve the above disadvantages, a blocking plate where a transmittance is changed according to a discoloration of a particle or a movement of a particle has been suggested. For example, a transmittance variable panel such as a liquid crystal panel, an electrophoretic panel, an electrowetting panel and an electrochromic panel having a variable transmittance may be used as the blocking plate.
When the liquid crystal panel is used as the transmittance variable panel, the transmittance of a transmissive mode is reduced due to the liquid crystal layer. In addition, when a color filter layer is used for various colors, a brightness is reduced. Further, since a blocking efficiency is relatively low, a contrast ratio is reduced.
The electrophoretic panel uses an electrophoresis where charged particles move according to application of a voltage. For example, black charged particles may move onto a transparent electrode to block a light when a voltage is applied, and white charged particles may move onto the transparent electrode to transmit or reflect a light when an opposite voltage is applied. As a result, the electrophoretic panel may have a blocking mode when the voltage is applied and may have a transmissive mode when the opposite voltage is applied. However, it is difficult to uniformly disperse black and/or white electrophoretic particles in an electrolyte layer. In addition, when a fluid is used for the electrolyte layer where the electrophoretic particles move, the electrophoretic particles may leak to an exterior.
When the electrowetting panel is used as the transmittance variable panel, it is difficult to fabricate the transmittance variable panel using a black oil. In addition, an extraction of a black dye or a black pigment and a leakage of a fluid such as an oil for displaying a color may occur.
The electrochromic panel uses an electrochromic material whose color is reversibly changed by an oxidation-reduction reaction according to an applied voltage. For example, an electrochromic smart window where tungsten oxide (WO3), molybdenum oxide (MoO3), neodymium oxide (Nb2O5), titanium oxide (TiO2) or tantalum oxide (Ta2O5) is used as an electrochromic material is suggested in Korean Patent No. 10-1535100. However, the inorganic electrochromic material has a relatively low response speed and requires a relatively high driving voltage for color variation. In addition, when the inorganic electrochromic material is applied to a window type display device or a vehicle type display device, an additional infrared (IR) cut film is required because the inorganic electrochromic material can not block an infrared ray.